A lone gunman began shooting Friday in an immigration services building in Binghamton, New York, killing at least four people, a law enforcement source close to the situation said.
The source said more than a dozen were wounded.
The man began shooting in the American Civic Association, which helps immigrants and refugees, the source said.
The source said a citizenship test was being administered in the building, but it was not immediately clear whether the shooting occurred in the area where people were taking the test.
The source said there may be 20 to 40 people who have been taken hostage.
The local newspaper, the Press & Sun-Bulletin, said on its Web site that at least four people were shot and 41 people had been taken hostage.
It said sharpshooters from the city's SWAT team were poised outside the building.
Video from the scene showed a person on a stretcher being taken to an ambulance. Watch interactive view of shooting scene
The Press & Sun-Bulletin said about 10 people came out of the building shortly after noon. They emerged with their hands on their heads. The police searched some of them, the newspaper reported.
Around 12:40 p.m., another 10 -- clad in white sheets -- came out of the rear of the building, the newspaper said.
Frank Rozboril, a spokesman for Our Lady of Lourdes Memorial Hospital, which is in the city, said the hospital had one person who had been at the association in the emergency room. Rozboril said the patient, who arrived around 12:30 p.m., was being assessed.
FBI spokesman Richard Kolko said the FBI is sending hostage negotiators and an evidence response team to the scene. The agency has an office in Binghamton, and agents are being sent from offices in Albany and Syracuse as well.
The newspaper said the incident began around 10:30 a.m. ET. Nearby apartments were being evacuated and Binghamton High School is on lockdown, it said.
"Within minutes [the situation] turned into one just flooded with police," Bob Joseph, news director of WNBF Radio, told CNN.
The American Civic Association helps immigrants and refugees with a number of issues, including personal counseling, resettlement, citizenship and reunification, and provides interpreters and translators, according to a United Way of Broome County Web site, which is affiliated with the association.
Rashidun Haque, who owns a nearby convenience store, said police had him and his four customers stay inside and away from the windows.
"I'm really shaky because this kind of thing -- it's a small city, it's a beautiful city -- but nothing goes down serious like this," Haque said.
He said the Civic Association building is about a two-minute walk from downtown.
New York Gov. David Paterson issued a statement saying it was "a tragic day for New York." He said he had directed state police to assist the Binghamton Police Department. "I speak for all of New York when I offer my prayers for the victims and families of this tragedy," Paterson said.